Sky - cerulean blue. Try to make it the right color for your painting ,possibly with violet or ultramarine. Paint at different angles, creating some variance in texture for the sky. Use square edged brush so you can trim up any leaning buildings.

For a tree ,he drags the paint in at an angle, then adds spots of color like light coming through the branches. (I have no tree.)

Yellow ochre and a bit of cadmium to warm it up more to do warm sunlit building. Start with white then add color mixture bit by bit. Start painting the edge of a building, going down, quite lightly so the undercolor shows up and gives texture. Never do a pure white - dirty white at best. All of these triangles to add in.

For windows, where they are in the sun, mix viridian into your sky color. If it has a white stone surrou.d, do a white mixture and apply it with the edge of a brush. Same technique for some roof edges - mix a gloomy (greyer) color to get the same effect in the shadow.For people: Canaletto used ochre and white for faces. Not skin tone, just the idea of faces, dots for eyes. A few streaks to add a shawl or a cloak, then stripes ,scraped in if necessary.

Draw in some pavement ... use some stripes for tiles on the rooftops ... Yellow ochre & cadmium red for San Giorgio Maggiore ...